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Introduction
Anterior cerebral artery (ACA) is one of the main terminal branches of intracranial internal carotid artery (ICA) [1, 2]. ACA shares in the anterior circulation of circle of Willis (CW) [3, 4].
Anomalies or variants of ACA include aplasia, hypoplasia and variations in number [5, 6]. In reported studies, the commonest anomaly of ACA was aplasia or hypoplasia of A1 segment of ACA [7, 8].
Incidence of aplasia and hypoplasia of A1 segment of ACA were 6.7% and 3% respectively at magnetic resonance angiography (MRA) in adults [9, 10].
While in autopsy, hypoplasia of ACA was discovered in 10% of cases and aplasia was noted in 2% of cases [11].
Many studies stated that anomalies of ACA were related to serious clinical implications due to co-existence of aneurysms and brain infarctions with ACA variants especially with azygos ACA as a consequence of hemodynamic instability [12-15].
Materials and Methods
This study is a retrospective observational cohort study. Institutional ethical approval was not necessary due to retrospective nature of the study. The study included 49 adult human subjects with ACA anomalies on brain MRA examinations. The study was conducted during the period from February 2015 till April 2023.
Of 74 brain MRA cases, forty nine cases were with anomalies of ACA in cerebral MRA and twenty five cases were with normal brain MRA. The cases were referred from outpatient clinics to department of Radiodiagnosis in Kasr Alainy Hospital, Cairo University. All cases performed magnetic resonance imaging (MRI) of the brain and cerebral MRA on 1.5 Tesla (Achieva; Philips Medical System) using head coil.
Data acquisition
MRI brain: Axial T1WI: Time of repetition/time of echo (TR/TE): 488/15, T2WI: 3,732/100, FLAIR: TR/TE/time of inversion (TI): 6,000/120/2,000, coronal T2 and sagittal T2. Field of view 24 cm, 256×256 matrix, 6 mm slices thickness, 1.5 mm slice gap.
Three-dimension time of flight MRA (3D TOF MRA): TR/TE: 25/6.9, flip 20, 160 slices. Field of view: 160 mm, thickness 1 mm, and matrix: 512×512. Maximum intensity projection (MIP) axial images were generated.
3D TOF MRA and maximum intensity projection images were evaluated for anomalies of the ACA, associated aneurysms and ICA stenosis. Magnetic resonance brain images were reviewed for any associated brain infarctions.
All procedures followed were in accordance with the ethical standards of code of ethics of the World Medical Association (Declaration of Helsinki).
Statistics
Odds ratios and relative risk were calculated to determine risk of occurrence of cerebral infarctions in patients with different types of ACA anomalies using Fisher’s exact test. Data were expressed as number and percentage of cases. Chi square test was used to assess the association between categorical variables. A P-value <0.05 was considered significant. Statistical analysis was performed with Statistical Package for the Social Sciences (IBM SPSS Statistics version 29; IBM Co.).
Results
The commonest anomaly of ACA in the current study was hypoplasia of A1 precommunicating segment of ACA which was predominantly right sided (Table 1, Fig. 1).
Insignificant association between morphological variants of ACA and patients’ sex was noted (Table 2).
Although insignificant association between azygos, hypoplastic ACA and cerebral infarctions was observed, but risk of occurrence of brain infarctions was higher in patients with azygos ACA than that in hypoplastic ACA (Table 3).
Multiple MRA views were mandatory to identify common trunk of bihemispheric variant of ACA (Fig. 2).
One case with saccular aneurysm was noted within distal A2 segment of azygos ACA representing 2% of total patients with ACA anomalies (Table 1).
Combined anomalies of anterior and posterior circulation of CW were noted in five cases (10.2%) with ACA anomalies which were combined aplastic/hypoplastic A1 segment of ACA and hypoplastic proximal posterior cerebral artery (PCA).
Discussion
In the current study, hypoplastic ACA was the commonest anomaly of ACA which was in discordance with Uchino et al. [19], who deduced that aplastic ACA was the commonest variation of ACA. Also, the former study had limitations in detection of bihemispheric ACA. In the present study, bihemispheric ACA was the least common variant of ACA.
In the present study, cases with right sided hypoplastic ACA were more common than left sided cases with high male preponderance which coincided with other studies [20, 21].
Zampakis et al. [22], investigated the role of computed tomography angiography in detection of cerebral arterial anomalies and found that hypoplastic ACA was more common than aplastic ACA with incidence of 27% and 9% respectively which was in agreement with the current study.
In the present study, there was no adult cases with triple ACA. Triple ACA, is a third artery that originates from AcomA with normal A2 segments of ACA presenting a rare incidence of 1.3% in MRA and autopsy studies [9, 23].
Some researchers identified the presence of few incidental cerebral aneurysms in association with azygos ACA reaching to 11% which accorded with the current study [19, 24, 25].
Infrequent incidence of cerebral infarctions 2% was reported by Uchino et al. [19], in association with ACA anomalies mostly with aplastic ACA. While in the current study, a slightly higher percentage of 6% was noted for ACA variants who sustained brain infarctions.
Clinically significant pathologies including brain strokes could be associated with azygos ACA. Anomalies of ACA could predispose to bilateral infarctions as in occluded azygos ACA or unilateral cerebral infarctions due to wandering of thrombi into the hypertrophied contralateral segment of ACA in cases with aplastic and hypoplastic ACA [26-28].
ICA stenosis and atherosclerosis have been described in association with anomalies of ACA especially with hypoplastic ACA [29, 30]. While in the current study, few cases with ICA stenosis existed together with hypoplastic and azygos ACA.
In a large cross sectional MRA study analyzed by Hindenes et al. [31], combined anomalous ACA and hypoplastic or missing proximal PCA was noted in 1.1% of cases with variations in CW. While in the current study, combined anomalies of ACA and hypoplastic proximal PCA were noted in 10% of cases with ACA anomalies. Inconsistency with the previous study was due to different sample population.
Limitations of the study were relatively small sample size and rarity of the cases. Strengths of the study were the foremost capabilities of brain MRA in evaluation of ACA variants by providing images of high definition and improved tissue contrast.
In conclusion, MRA was highly reliable in identification of different anomalies of ACA and concomitant vascular changes.
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